1. Field of the Invention
The present invention relates generally to electrophotography and, more particularly, to a pneumatically powered, toner delivery system particularly suited to a multicolor electrophotographic apparatus using liquid toners.
2. Description of the Related Art
Electrophotography employs the formation of an electrostatic latent image to create a hard copy reproduction. In its basic aspects, a substantially uniform charge is applied to a photoconductive insulating surface area of a photoconductor. The charged surface area is exposed to a pattern of light. A latent image of the pattern formed on the surface by charge dispersion is then developed by application of electroscopic toner to the photoconductive material. The developed image is transferred to a hard copy medium and fused to the medium. The photoconductive material insulating surface is then cleaned and reused for the next image. This basic construct is used in the state of the art in variety of products such as computer printers and plotters, copiers, facsimile machines, and the like.
In the field of hard copy reproduction such as with a laser printer using liquid electrophotography techniques to provide full color printing and plotting, yellow, magenta, cyan (the subtractive primary colors), and black liquid toners are employed. These toners present challenging design problems. One such problem area is in designing a system for delivery of such liquid toners from reservoirs to developer devices of the apparatus where toner is transferred to the photoconductor.
Typical color electrophotography liquid toner delivery subsystems employ separate pumps connected to refillable, or replaceable, toner reservoirs. Such pumping systems require either separate motors or complex gearing to drive the pumps. Each toner reservoir requires disconnect mechanisms and a vent system which can be relatively expensive components. Thus, liquid toner delivery subsystems are a complicated and relatively expensive component of the hard copy machine.
Two inherent problems with such subsystems include pump gear freeze-up and leakage of toner from seals. Dried toner residue may contaminate moving parts of a pump.
Additionally, upon replacement of the toner, the pumps will have some contamination from the previous batch. Therefore, to alleviate this contamination, the pumps must either be cleaned prior to a toner refill or, more expensively, replaced with a completely new toner cartridge. Because of the nature of the toner chemicals, any leakage is a potentially messy problem. Moreover, a toner reservoir vent must be open during operation and dripless during shipment even under changing atmospheric conditions. That is, the vent (along with the reservoir container and quick-disconnects) must pass air without leaking toner and be able to withstand up to approximately six pounds per square inch ("psi") pressure differential for extended periods of time without leakage.
Therefore, there is a need for a liquid electrophotography toner delivery system capable of cleanly delivering four different colors of liquid toner to respective developers. The system should operate in both a reliable and leak-free manner.
Furthermore, the system should provide a simple, clean, and inexpensive toner replacement mechanism. The system should utilize a toner reservoir cartridge that can be shipped commercially and thus be able to accommodate changes in atmospheric temperature and pressure.